1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to radio frequency identification and, more particularly, to a tag for radio frequency identification for measuring temperature of an object with the tag and transmitting the measured temperature together with identification data needed for identification.
2. Description of the Related Art
The recent development of radio technology leads to various radio frequency identification (RF-ID) systems, such as simple prepaid bus traffic cards and pass cards for parking lots and research institutes.
FIG. 1 is a schematic diagram illustrating a configuration of a general radio frequency identification system. Referring to FIG. 1, the radio frequency identification system is largely composed of a tag 10 and a reader unit 20. The tag 10 may be fabricated in the various forms such as a card, a sticker, or the like depending on a user's convenience and use.
Radio frequency identification is basically accomplished by radio frequency signal exchange between the tag 10 and the reader unit 20. Specifically, an integrated circuit (not shown) embedded in the tag 10 reads information needed for identification from an internal memory and outputs the information as a radio frequency signal, and the reader unit 20 receives and confirms the information.
The radio frequency identification system may be classified into an active radio frequency identification system or a passive radio frequency identification system, depending on a driving manner for the integrated circuit (IC) embedded in the tag 10. The term active means an IC driving manner that uses a battery embedded in the tag 10, and the term passive means an IC driving manner that induces current from a magnetic wave, which is received from the reader unit 20, and uses the induced current to drive the IC.
In many applications, the passive radio frequency identification system having no battery is used, allowing a thin light tag 10. The tag 10 includes a coil therein in order to implement the passive radio frequency identification system. The coil serves as an antenna that derives current from the magnetic wave received via the reader unit 20 and transmits identification data as a radio frequency signal needed for identification. The input signal derived at the coil is converted to a given size of constant voltage and the constant voltage is applied to the IC, to drive it. The conversion of the input signal derived at the coil to the constant voltage needs a rectifier. The rectifier may be implemented using a voltage doubler, or the like. The IC, driven with the constant voltage, reads out identification data stored in the internal memory and transmits the data as a given radio frequency signal via the coil.
Meanwhile, use of a typical p-n diode to implement the rectifier for the tag 10 significantly degrades efficiency of detecting a low-power input signal because of a high forward turn-on voltage of the p-n diode. To prevent the degradation of the detection efficiency, use of a schottky diode, having a low forward turn-on voltage, has been actively studied. In particular, a radio frequency identification system operating at a high frequency band has been recently developed for use in a variety of industrial fields, such as an article conveyance system. In such a radio frequency identification system, it is common that the schottky diode is used to make the tag.
In order to send, for example, temperature data in addition to the identification data needed for identification, a sensor is included in the conventional tag 10, and data measured by the sensor is transmitted together with the identification data. In this case, the inclusion of the sensor increases the size and manufacture cost of the tag 10. Furthermore, additional power loss is caused by the sensor.
Meanwhile, the schottky diode has a characteristic that a change in temperature leads to a change in impedance, voltage sensitivity, and the like. In particular, since the voltage sensitivity becomes degraded as the temperature becomes higher, output voltage from the schottky diode is reduced in size. Thus, power efficiency is degraded in high-temperature environments.